Mercury-arc-rectifier cathode construction



Oct. 10, 1933. E. e. SHAND MERCURY ARC RECTIFIER CATHODE CONSTRUCTION Filed April 4, 1930 were connected.

- ing the rectifier tank. I

Patented Oct. 10, 1933 ,wm I

- IMERCURYQARGRECTIFIER oA'rHonE CONSTRUCTION- Errol B. Shand,'Pittsburgh, Pa, assignor to Westinghouse Electric & Manufacturing Company, r I l a corporation of Pennsylvania r Application April 4, 1930. Serial to; 441,683

'1 Claims. (01. 250 -215) My invention relates to metal-tank mercury-arc 4 rectifiers and more particularly toelectrodesfor Prior to my invention, considerable diiiiculty I has been experiencedwiththeseal -for cathodes for mercury-arc rectifiersp Rubber seals are easy to make vacuum-proof but have given trouble in that they give off gases at the high temperature at which it is necessary to operate the material about the electrodes of such rectifiers.

have withstood the heat very well. However, when solder seals areused, 'it'is very inconvenient to remove'and replace the'cathodes without disconnecting and upturning; the tanksto which they My invention makes possible the elimination of difliculties of both of these seals and provides'a cathode assembly whichmay be easily dismantled from the tank either in the shop orin the field without the necessity of disconnectingor invert- It is an object of my 'inventionto provide'an improved cathode assembly for a mercury-arc rectian improved seal for such cathode assembly.

' the insulator ring and the metallic portion of the Both the upper and lower platesare provided witha plurality of openings.. These openings are provided withbolts '15 for clamping the upper and lower cathode plates into firm engagement with the ring insulator 10. These bolts are provided withinsulating sleeves 16 and collars 17 to 1; I

insulate'the bolts thoroughly from the bottom cathode plate. Also, an insulating cap 18 is preferably provided to be placedover the. clamping nuts on the bolts." '9- A packing 20 of asbestos or other heat-resisting material is generally. placed at each end of the insulator ring 10 in order to equalize the pressure between the cathode plates and the ring. This packing serves a further purpose in that itprevents mercury from passing into any capillarity,

spaces between the insulator ring and the cathode plates.

After the cathode plates have. been clamped against the insulator ring, a'semi-permanent sol-.

der seal is made between each of the cathode plates and the insulator ring.

This seal may be made in several ways. Solder could be applied directly to, a prepared surface on plate. However, I prefer to first provide the insulator ring, at both top and bottom, with'a tinned Other-objects and advantages of my invention willbe apparent fromthe following detailed de-' scription, taken in connectionwith the appended drawing, in which the figure is a sectional eleva tion'of a cathode embodying my invention.

The apparatus disclosed in the drawing come prises a base member 1 for a cathode assembly having a cup-shape depression 2 in the upper face thereof to receive a' mercury cathode pool 3. In operation, this cathode pool will be heated by the rectifying arcfroma plurality of ano'desinot shown) 7 It is desirable, therefore, to provide means for cooling-this electrode. To this end, a

' Tdownwardly projecting ridge or flange 5 is provided on the under 1 part of the cathode plate. A

closure 6 is attached, preferably by: screws 7, to 1 this ridge to provide a, closedchamber in the bottom of the cathode plate.

The closure plate 6 is provided with a plurality of openings 8 and 9 to permit the inlet and the egress of cooling waterto andfrom the'closed chamber.

of the mercury pool 3. Resting on this insulator,

is a top cathode plate 12'having an aperture 13 therein substantially equal in diameter, to the diameter of theicathode pool.

side of the insulator-ring near the top and bottom copper flange 21 which is soldered to especially prepared metal-glaze surfaces 21a and 21bon the thereof, respectively. 'Also, both the top and.bot- .51; tom cathode plates are provided with tinned coppergflanges 22 which have been soldered to the plates before assembling. Thereafter, when the plates and the ,insulatorare assembled with the tinned copper flanges inproximity to each other, theytmay easily be soldered to each other to provide a vacuum-tight seal. f V

A cathode cylinder or are guide ,25, having a flange or baiiie 26 on the exterior thereof of sufficient size to just pass the central opening of the upper cathode plate, is placedv within the mercury pool. After the cylinder has been placedv 7 in position, a reducing member 30-is applied to the upper cathode plate to reduce the opening sufficiently to prevent withdrawal-of the guide cylinder 25 from the assembly. Usually, the reducing member will take the form of a ring-like 5 collar having its upper edge chamfered to provide a ready drain ofany mercury that'may collect-thereon. Preferably, both thereducing ring and the uppercathodeplate will be so cut as toprovide a ring seat 31 to which the ring maybe. screwed or otherwise secured in place. In order to hold the cathode cylinder firmly in place,

a clamp member 35 is preferably screwed or otherwise connected to the bottom of the cathode pool. The reducing ring 30, in conjunction with the baffle 26 and the cathode cylinder 25, serve two distinct purposes; first, it presents a restricted tortuous path between the cathode cylinder and the tank proper 40, so that the danger of the are striking in the space between the tank 40 and the cathode cylinder is materially lessened; sec ond, this breaks up any stream of mercury which might otherwise flow down the outside of the cathode cylinder 25, and thus preserves the arc ing distance in the rectifier. i

The metal tank 40 of the rectifier is provided with a jacket 41 adapted to contain water or other cooling fluid for the rectifier, Advantage is taken of this fact to provide a cooled surface against which a compressible rubber gasket 45 is applied to provide a vacuum-tight seal between the cathode assembly'proper and the tank of the rectifier. The upper cathode'plate 12 is provided with a shoulder 46 against which the rubber gasket may be assembled before the cathode assembly is seizured to the tank of the rectifier by means of screw studs 47 or other desirable fasteners.

It will be understood that the solder seal 21,.

22 which unites the several parts of the cathode assembly will be disengaged only when it is desired to dismantle the cathode assembly itself, or to replace a damaged portion in the assembly. These repairs will be made in the shop or factory, when it is most convenient to provide the necessary tools for performing the soldering opration. Any removal or replacement of the cathode assembly, as a whole, in the field, will be made with a minimum number of tools by disconnecting the screw studs 47 and the readily separable rubber seal 45 between the upper plate 'of the cathode assembly and the tank proper. Thus, the solder seals, which are made in the cathode assembly, will be of a semi-permanent nature, as contrasted with the readily separable rubber seal between the cathode assembly and the "tank of the rectifier.

In operation, my device has the advantage of both the heat-resisting qualities of the solder seals and the easy separability of a rubber gasket. The cathode, because of the high heat transmitted to it from the arc, is joined to the insulator 10 by means of heat-resistant solder seals. These seals may easily be placed so that they will receive sufiicient cooling to prevent being unsoldered .by-the heat of the cathode. The rubber seal is *then placediat a sufiicient distance from the cathode proper, so that the heat is materially reduced, or, if desirable, the upper cathode plate may be water cooled. Further, this rubber seal is placed against a cooled metal portion of the tank, sothat any heat which is transmitted to the rubber gasket will be dissipated before the gasket is raised to a sufliciently high temperature to emit troublesome gases.

I do not desire to restrict myself to the specific embodiment of my invention herein shown and described sinceit is evident that it may be changed and modified without departing from the spirit and scope of my invention as defined in the ap- 4 pended claims.

receiving the mercury pool, a second depression in the opposite face and concentric with said first depression, a cover for said second depression to provide an enclosed chamber in the face of the plate, a plurality of openings in said cover to permit circulation of water in said chamber, a ringshape top plate spaced fromthe bottom plate, an insulating collar of vacuum-tight material between the top and bottom plates, a vacuum-tight semi-permanent seal between the insulator and each of the plates, means for removably connecting the top plate to the rectifier tank, and means including a readily separable gasket for providing a vacuum-tight seat between the top plate and the tank.

v 2. A metal-tank rectifier comprising a tank proper, a bottom member adapted to contain -a pool of mercury,a water chamber in said bottom member to cool the pool of mercury, means for circulating water in said water chamber, an insulating spacing member on said bottom member, a ring-like top member resting on the insulating spacer, means for drawing the top and bottom members into firm engagement with the insulating spacer, a vacuum-tight semi-perma-,

nent seal between the insulating spacer and the top and bottom members to .pr ovide a cathode assembly, means for removably attaching the cathode assembly to the tank proper, and means comprising a compressible gasket for hermeticali ly sealing the cathode assembly to the tank proper. 1 3. A cathode assembly for a mercury-arc rectifier, comprising a bottom plate,v cooling means for said bottom plate, a ring insulator on said bottom plate, a top plate having an opening therein resting on said insulator, a packing between I each of said plates and said insulator, means for drawing said plates into firm contact with said insulator, means for insulating said drawing' means, vacuum-proof solder seals between each of the plates and the insulator, a ring fitting into the opening of the top plate to reduce the size of said opening, a pool of mercury in said cathode, an arc-guard in said mercury poolv and extending through said top plate, a clamp in said mercury pool and secured to the bottom plate for holding said arc-guard, a baffle attached to said areguard and spaced a short distance from the ring,

means for securing the cathode assembly to, a

metal tank and means comprising a rubber gas-.

ket for sealing the cathode assembly to the metal tank.

opening, a pool of mercury in said cathode, an arc-guard in said mercury pool and extending through said top plate, a clamp in said mercury pool and secured to the electrode plate for holding said arc-guard, and a baflie attached to said arc-guard and spaced a short distance from the ring.

5. A replacement cathode assembly adapted'to be secured as a unit to a metal-tank mercury-arc rectifier comprising an electrode member, a ring insulator resting upon the electrode member, a

opening of the top plate to reduce thesize of said I top plate having'a central opening therein resting upon the ring insulator, means for drawing the said top plate and the electrode member into tight contact with said ring insulator, a vacuumtight metallic seal between each of said plates and said insulator, a ring attached to said top plate to reduce the size of the central opening, and an arc-guard resting on said bottom plate and extending through said top plate.

6. A cathode assembly adapted to be secured as a unit to a metal-tank mercury-arc rectifier comprising an electrode member, a ring insulator resting upon the electrode member, a top plate having a central opening therein resting upon the ring insulator, means for drawing the said top plate and the electrode member into tight contact with said ring insulator, a vacuum-tight metallic seal between each of said plates and said insulator, a ring attached to said top plate to reduce the size of the central opening, an arcguard resting on said bottom plate and extending through said top plate, a'clamp on said bottom plate to retain said arc-guard in position, and

'a baffle on said aro-guard'for preventing a flow of mercury along the outer side of the arc-guard.

'7; A cathode assembly for a metal-tank mercury-arc rectifier comprising a bottom plate having a depression adapted to receive a pool of mercury, a top plate having an opening therethrough, an arc-guard in said cathode, a baille on said arc-guard capable of passing through said opening, means for reducing the size of said opening to I a size smaller than said baflie, means for securing said reducing means in position, a ring insulator between said plates of greater internal diameter than the opening in said top plate, a metallic vacuum- -proof seal between each of the plates and the ring insulator, means for securing the cathode assembly to the rectifier tank, and a compressible gasket between thecathode assembly and the tank.

ERROL B. SHAND.v 

